Diabetic nephropathy is clinically characterized by microalbuminuria and elevated glomerular filtration rate, followed by overt proteinuria and endstage renal failure. Several histological abnormalities develop; however, the progressive expansion of mesangial matrix is responsible for obliteration of the capillary lumena and loss of glomerular filtration. It is the purpose of this proposal to define those features of the abnormal metabolic milieu of diabetes that contribute to the development of mesangial sclerosis. Hypothesis: Insulin treatment, either directly or indirectly, contributes to the increased synthesis and altered phenotypic expression of mesangial matrix collagen which typifies the glomerulosclerosis of diabetic nephropathy. This hypothesis will be tested by the following specific objectives: Objective 1. Preliminary data have demonstrated that insulin treatment is associated with increased synthesis of mesangial matrix collagen and a change in the phenotype of collagen produced (type IV to type III). These observations will be confirmed by histomorphometric analysis of glomerular structures and analysis of expression of collagen phenotypes from saline and insulin-treated normal and diabetic rats. Objective 2. To define the specific influence of insulin and insulin-like growth factors (IGF) on collagen synthetic rates and profiles using cultured rat mesangial cells. Objective 3. To confirm that those factors which stimulate an increase in matrix synthesis and phenotype in vitro contribute to the accumulation of mesangial matrix in vivo. Correlations will be made between serum insulin, glucose and IGF values, glomerular production of IGF, and the degree of mesangial matrix expansion and type III collagen gene expression in tissues harvested from control and diabetic rats. Objective 4. To determine the biological effects of diabetically altered mesangial matrix on the function of mesangial cells. Attachment, proliferation and secretory phenotype of mesangial cells introduced onto normal and altered cell-free extra-cellular matrices will be determined. Definition of those metabolic factors which contribute to he development and progression of mesangial sclerosis should lead to strategies for the prevention of diabetic nephropathy.